<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #box{
      width: 200px;
      height: 200px;
      background-color: #c17373;
      margin: 20px auto;;
    }
    #box2{
      width: 200px;
      height: 200px;
      background-color: #2fb755;
      margin: 20px auto;;
    }
  </style>
</head>
<body>
  <div id="app">
    <div :class="a">1</div>
    <div :class="[a, 'box2', 1==1?'box3':'']">2</div>
    <div :class="{active: 1==1, b: false, c: true}">3</div>
    <div :class="[a, 'box2', 1==1?'box3':'', {active: 1==1, b: false, c: true}]">4</div>
  </div>
  <script src="./vue.global.js"></script>
  <script>
    const { createApp } = Vue;
    const app = createApp({
      data(){
        return {
          a: 'box'
        }
      }
    })

    app.mount('#app')
  </script>
</body>
</html>